1. Field of the Invention
The present invention relates to a method of forming an image on a roll of paper sheet as the paper sheet is transported stepwise in a sheet feed direction.
2. Description of the Related Art
There has been proposed an image forming device including a print head for forming an image on a roll of paper sheet. The print head is reciprocally transported across the paper sheet to form one line's worth of image on the paper sheet. In this type of image forming device, the roll of paper sheet is fed by a predetermined amount in a sheet feed direction each time one-line's worth of image is formed.
However, line feed operations for feeding the roll of paper sheet may not be performed precisely. As a result, the image may be formed with undesirable lines and gaps, thereby degrading quality of the image.
There is another type of image forming device which includes a print head reciprocally movable both in a head moving direction and in a sheet feed direction. With this configuration, the print head can form one region's worth of image, that is, a plurality of lines' worth of image, on the paper sheet without performing sheet feed operations. After one region's worth of image is formed, the paper sheet is fed by a predetermined amount. Then, the subsequent one region's worth of image is formed. In this case, it is unnecessary to perform sheet feed operations every time one line's worth of image is formed. That is, the sheet feed operation is performed less often. Therefore, undesirable lines and gaps will be less likely formed on the image.
However, in this case also, such undesirable lines or gaps may not be prevented completely. Specifically, as shown in FIG. 1, when sheet feed operations are not performed precisely, a character image 200 straddling two print regions of a paper sheet may be formed with an undesirable blank line 200a or a gap.